"Disease gets a bad rap, don't you think? For being filthy. Chaotic. Uh, but, really, that just describes people who get sick. Disease itself... Very...Pure...Single-minded. Bacteria have one purpose --divide and conquer. That's why, in the end...It always wins."

Pestilence, also known as the Green Horseman or Sneezy, is an extremely powerful entity and is also one of the Four Horsemen of the Apocalypse, embodying illness and irritation amongst humans. Pestilence is affiliated with his brothers Famine, War and Death. Due to modern times and technology, Pestilence travels in a green Hornet Wagon which represents his green steed. He manifests physically on Earth by mimicking human form.

Pestilence first appears as a sickly old man, but he later reveals himself as a powerful figure. Like War, Pestilence was shown to be a good actor, able to pass himself off as either a sick man or a kindly doctor. He has a strong relationship with his brothers, and he is willing to defy Lucifer's orders over what Sam and Dean had done to his brothers.

He also has a low view of humans, not caring how many he kills and even doing so casually, much like an experiment. However, Pestilence implies he is somewhat jealous of mankind, evidenced by his statement "So I wonder why God pours all his love into something so messy and weak!". Unlike his brother Famine, Pestilence did have some care for demons, after scaring one of his demonic helpers, he comforted her before continuing his business. Despite this he can be very hard on them, particularly when they fail to meet his expectations.

Pestilence also had a habit of hiding his feelings, and appearing calm and even friendly, then in mid conversation letting out his true feelings, in one or two explosive bursts. Pestilence also shows no fear of defying Lucifer. Even when a demon points out they have orders not to harm Sam or Dean, Pestilence shows no consideration and merely states that Lucifer will just have to "glue them back together."

He also admires bacteria, stating how they are single-minded and focused on their goal, saying "and that is why, in the end it always wins."

Even though he is the youngest Horsemen and being the personification of the concept of sickness, Pestilence is very powerful, and unkillable as a Horseman. And, like his brothers, he requires his ring to help him focus his powers. A testament of his power was when he shouted on a supernatural level at his demon servant, and she was completely terrified.

Biokinesis - Pestilence can create, manipulate, and control diseases, plagues, infestations, molds, and other ailments. He can also cause instantaneous illness in another being. Pestilence possesses dominion over ailments. His sickness powers don't work on angels, and was fascinated when they affected near-human Castiel.

Indestructibility - Pestilence himself, as a Horseman, cannot be physically destroyed. Pestilence, like the other riders, requires a ring that channels his essential core abilities.

Teleportation - Pestilence can go anywhere he chooses in the universe.

Cosmic Awareness - As a horseman, Pestilence possesses an incredible amount of knowledge and understanding of the universe and its workings, although his knowledge is vastly inferior to Death's. He can understand concepts, such as the Apocalypse and nature of sickness.

Though literally, nothing in existence can kill or destroy Pestilence if his attribute still exists, he has some weaknesses.

Ring Removal - Without his ring, his corporeal form loses all its powers, except for teleportation.

Physical objects - Anything serrated or jagged, or for that matter anything that can be implemented into a weapon, that can be used to pierce can inflict pain upon Pestilence's physical form. His physical body can be pierced and penetrated identically to how humans sustain infliction.

God - While even God can't kill him, God can do absolutely anything else to Pestilence.

At a small drug store, a large fly lands on the clerk's desk as the clerk reads about a viral epidemic that has been going around the area, but before he can swat it, Pestilence enters the store, hacking and coughing up gobs of a disgusting mucus and spreading it all over everything in his reach as he looks for some flu medicine. When he takes it to the counter, he sneezes more of his mucus into the clerk's face, likely infecting him with the latest virus he has been spreading in the area. When Pestilence leaves the store, he gets in his sickly green beaten-up Mustang, tosses the medicine aside and smiles to himself as a swarm of flies fill his car all around him, revealing that his "illness" is merely a ruse so he can spread his diseases and infect as many people as he possibly can.

Like his fellow horsemen, he has been busy spreading his influence across the land, and according to the paper the clerk is reading, he has already spread several contagious diseases in the area. When in the disguise of an ill traveler, he tells the clerk he still has "a lot of driving to do", implying he has many more tricks up his sleeve.

Since the previous episode, the brothers have been chasing after him, always one step behind him. But with help from the demon Crowley, the brothers make a plan to get his rings. The boys learn that he has been causing mass outbreaks of the Swine Flu, something the brothers find strange because Pestilence could do much worse, such as the Croatoan Virus for example. It is revealed over the course of the episode that the Swine Flu outbreak is part of a bigger plan Pestilence is working that will eventually involve the Croatoan Virus. Having infiltrated a major drug company, his servant Brady and a few other demons have begun testing the virus on unsuspecting humans in the labs at night, with the eventual plan being to disperse the virus among regular Swine Flu vaccines to cause a mass outbreak.

Though not seen in the episode, Brady communicates with Pestilence through the use of an identical goblet filled with blood of a human victim, similar to the method used by Meg Masters. While we do not hear his voice, several flies appear from the goblet, and Brady explains that the trials are proceeding as expected, but that they must be careful as to not arouse suspicion. Pestilence seems pleased with the news, but informs Brady that should he fail, he can always find another demon to replace him.

In the beginning of the episode, Pestilence is revealed to be hiding in a retirement home, posing as a "Dr. Green". He is seen examining an elderly patient, infecting her with various diseases and observing the effects they have on her before she dies. When he is alerted by a demon posing as a female nurse that the Winchesters are here, he decides to infect them with various diseases, despite the demon's reminder that Lucifer has ordered them not to be harmed. He greets the Winchesters as they stagger towards his room, suffering from Pestilence's powers and has the demon nurse bring them into the room. He goes on to tell them that he prefers diseases to people, and how he can't understand why God loves something so "messy and weak". As he moves in to finish them off, Castiel arrives and Pestilence is surprised to find that the low-powered angel is now susceptible to his powers. Despite his weakened condition, Castiel manages to cut off his ring finger and kill the demon nurse. As his powers begin to wear off of the trio, he says "It doesn't matter. It's too late," before vanishing.

Sam and Dean later learn that he referred to his and Lucifer's plan to spread the Croatoan virus through shipments of swine flu vaccine. Sam, Castiel and Bobby Singer foil his plan by killing his demons and blowing up the distribution warehouse before the virus can be sent out.